1. Field of the Invention
The present invention relates to an ultrasonic speckle velocity measurement method and apparatus, more particularly to an ultrasonic speckle velocity measurement method and apparatus for detecting the velocities of moving members comprised of random scattering bodies, within a subject under examination, not through the detection of frequency shift information produced by the Doppler effect but by a novel method which uses amplitude fluctuations (speckles) in the received signals resulting from random interference between the ultrasonic waves scattered by the scattering bodies.
2. Description of the Prior Art
The ultrasonic Doppler method is a well-known method of measuring the velocity of moving members, such as for example the blood flow, in a subject. The ultrasonic Doppler method utilizes the fact that the motion of a moving member produces a frequency shift in the carrier frequency of a transmitted ultrasonic wave, i.e., the frequency shift corresponding to the velocity of the moving member. Therefore, by detecting the frequency shift from the center frequency of the reflected echo signal, the velocity distribution of the moving member can be displayed in real time on a display screen or the like.
However, with this type of ultrasonic Doppler method it is difficult to measure the velocity of moving members that are moving at a relatively low velocity. That is, with the ultrasonic Doppler method it is the frequency shift in the carrier frequency of the echo signal that is detected, but in the case of a moving member that is moving at a low velocity, the degree of frequency shift is extremely small, and detecting this small degree of frequency shift from the echo signal, which is obtained as a time-series signal, is extremely difficult.
Another drawback when the Doppler effect is utilized is that it is only possible to measure the velocity of the movement of a member which includes velocity components indicating a movement toward or away from the direction in which the ultrasonic wave is transmitted. The method cannot detect the movement velocity of a reflective member that is moving in a direction perpendicular to the ultrasonic wave, for example, when a single transducer is being used for transmitting and receiving the ultrasonic wave.